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Author Topic: Homebrewing pitfalls .. (editorializing)  (Read 3836 times)
KC9KEP
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« on: February 11, 2013, 06:25:12 AM »

Hello all,

I felt compelled to editorialize for a moment about home brewing (at about least vacuum tube equipment.)

Some of the most important aspects of fabricating homebrew equipment seem to be glossed over in the vintage ARRL articles.  Although the ARRL handbooks make what I consider to be casual references such as: Shield power supply leads, route control cables along chassis edges, keep input & output leads away from each other, these concepts seem to be critically imperative and should really be emphasized.

Although it’s water over the dam now (and probably trivial to those who have spent time in the trenches) for neophytes such as myself, these “gotcha’s” get me .. time and time again!

Of course, those with experience will recognize that the schematic diagrams are laid out to facilitate functional understanding of the circuitry.

I recall building the ARRL’s 1944 receivers and wondering why two capacitors would appear connected to a single wire lead in two different places.  “Why not use one capacitor of twice the value?”  Of course, they were trying to emphasize separate bypass capacitors for two places in the same circuit.

As W8JI said somewhere, “we must stop treating [RF] systems like they were DC systems”.

This morning, I stumbled upon the following article;  ARRL’s “Single Sideband” circa 1965 “Some Notes on the ‘Single Sideband Package’”

The article is similar to a recall of the preceding feature article.  It points out several pitfalls in the initial publication.  They’ve added steps such as:  mounting a metal plate across the [driver] socket between grid and plate prongs and grounding it, this stage was made stable”.

And in Ted Crosby’s HBR-11(which I had built), a construction techniques post-feature-article of tips on connecting components to the miniature tube socket were published.  The technique is to solder a 1” length of 14 gage wire vertically to the socket’s center ground provision and mounting components vertically to this grounded center lead.  Additional tips are shown for keeping front-end RF leads short, direct and made of 14 gage wire and so on.

So, I appears that others have been “bit” by these pitfalls as well.

At any rate, I just felt compelled to vent a bit.  I think I have spent more time chasing some of these instability issues than I did building the entire projects.  And I think the handbooks could have pointed these pitfalls in terms such as:  “The following layout is critical.  This circuit will not operate correctly unless you do the following ..” type of stuff.

But thanks to all who have been Elmering me along.   I will not be making some of these mistakes again!

73

--KC9KEP
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AA4PB
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« Reply #1 on: February 11, 2013, 07:11:53 AM »

The definition of experienced is when you've been bitten by most of the possible pitfalls and are still young enough to remember what they were  Grin

I'd say that modern solid state design with printed circuit boards has even more pitfalls than the old tube type designs. Speed has increased so much that many digital circuits now need to follow some RF design techniques when it comes to PC board layout. The schematic will tell you what parts are used and how they connect but not the critical physical layout including part positioning, ground plane layout, etc.

I remember many years ago when a friend and I built a 1KW 6M AM transmitter from an ARRL Handbook design. It worked great until about 10 minutes into the first QSO when the tank coil got hot enough to melt the solder and dropped to the bottom of the chassis! The lesson learned - use copper tubing for the coil and don't depend on solder to support it.
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KC9KEP
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« Reply #2 on: February 11, 2013, 08:17:18 AM »

LOL!

Great stuff .. I hear you brother :-)

73

--KC9KEP
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G3RZP
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« Reply #3 on: February 11, 2013, 10:14:23 AM »

AA4PB said:

>Speed has increased so much that many digital circuits now need to follow some RF design techniques when it comes to PC board layout.<

That was certainly the case back in the early 1980's, and I wrote a section on printed circuit design in the Plessey Semiconductors' High Speed Dividers Data book. Called, strangely, enough 'The Care and Feeding of High Speed Dividers' - somewhat on the lines of General Booth who started the Salvation Army and said 'Why should the devil have all the best tunes?' From which you can tell that I am a tube man at heart, even with 32 years in semiconductors!

In those days, we were dealing with dual in line packages going up to 3 GHz. Later on, we had that well known microwave package, the 8 lead MINI-DIP, working with a 10GHz divide by 10. But ECL is now about as out of date as germanium.....although it was far better on phase noise than GaAs.
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KB1WSY
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« Reply #4 on: February 16, 2013, 09:49:50 AM »

Tnx KEP, a useful insight. Over the past year I've been collecting the parts for several vintage ARRL projects but just haven't had the time to do much building. One of the interesting things is how relatively hard some of the projects are, even some of the "novice" projects, once you read the articles carefully. The coil lists and instructions look clear until you actually start building them (which I have). You have to figure out a lot of stuff on your own. Which of course is what homebrewing is all about, if you think about it, and I'm looking forward to learning from my mistakes when I can finally carve out time -- which may be years from now at this rate.

BTW I particularly admire your custom chassis work; I think you are using a brake and making them from scratch right? It looks like nice, thick metal.

73 de Martin, KB1WSY


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KB1GMX
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« Reply #5 on: February 16, 2013, 03:29:02 PM »

I've been building with every technology available since the early 1960s.  The things I've learned.

The RAH especially the ones In the 50s through 70s really must be read cover to cover.  Its in the
early and some of the late pages where those "details" are covered.  That and looking at any pictures
of successful ones. 

In the end if its not a full kit (as in heathkit or Elecraft) then experience is a critical factor in how it
will behave, or not.  The more it depends on the builder to fill the blanks or package the more likely
the builders knowledge is needed to complete it. 

With that said I've built a few kits that were questionable design to start with.  In the end I build a
lot and there is a lot of "things you just got to know" if they are not part of the article.  IF they don't
say so and it's important guess who discovers it?  The builder.


Allison
 
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N2EY
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« Reply #6 on: February 21, 2013, 12:29:51 PM »

Random observations:

- There's a very good article called "Just Like QST, Except...." in the March 1959 issue of QST. It details how little things can make a big difference.

- When you see a project in a book or mag, remember that they probably built just 1, or maybe 2. It worked OK and they wrote the article. Not even ARRL has the resources to do a prototype run of, say, 100 copies to find all the little things.

- Sometimes using the exact same part is critical, sometimes it isn't. When is not obvious. Sometimes substitutions are fine, other times they are the source of the trouble. This is particularly true when things like distributed capacitance, Q, lead inductance and such are involved. I have encountered cases where a ferrite-core RFC wouldn't work but an air-core did. Etc.

- Always be on the alert for typos, drafting errors, math errors, etc. They don't all get corrected.

- Schematics are only part of any design. Layout, parts selection and other factors are as if not more important.

- Start off simple and work up. Understand what you're building before you start. It may even make sense to build a prototype on an old chassis to prove out a design.

- Test all parts before installing. New or old.

- Read old QSTs, Handbooks, Understanding Amateur Radio, RSGB Handbook, RCA tube manuals, etc. They are an education in themselves.

73 de Jim, N2EY
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G3RZP
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« Reply #7 on: February 22, 2013, 02:43:48 AM »

Measure every carbon resistor before installing it. Some 5 or 6 years ago, I took a brand new, never been used, 1964 packed, 1/4watt, 5%, 4k7 carbon comp resistor out of its two Nato packaging plastic bags. It was over 20% high in value.....
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K8AXW
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« Reply #8 on: February 22, 2013, 11:22:00 AM »

Things I've learned during 50+ years of building include NOT building anything written up in QST until at least 3 months have passed.  This give the author time to proof read his work after publication and send in corrections via "Strays." 

I've had good luck with circuits built from the ARRL Handbook.

I've had a major problem with the ARRL HBC (Home Brew Challenge) projects because when ARRL rates their winners and runners-up they don't take into consideration 'ease of replication.' 

It pays to spend some time mentally building the project to determine if you can actually do it.

For example, if a project uses point-to-point wiring with several ICs, then you need to determine if you're going to wind up with a "rat's nest" of wire which is extremely difficult to troubleshoot and or find mistakes.

Before actually buying one component, I source all of the parts and keep a cost sheet for everything needed to do the project.  During this process I've found that in many cases some components, especially solid state  devices are obsolete or some part was a onetime thing available at some surplus outlet. 

I've also learned by sourcing parts first that the final total cost is more than what the final product is worth.

Homebrewing is my favorite part of ham radio but it pays to start with simple projects and work you way up over a long period of time.  Pitfalls are plentiful but shouldn't be a deterrent.
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W1JKA
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« Reply #9 on: February 22, 2013, 11:51:26 AM »

Piftall Memories:

  As one of the many financially challenged young novices of the late fifties I was regulated to all homebrew gear,regens,converted am radios,1 tube xtmrs., tuners, power supplies etc..All parts courtesy of junked televisions,radios, electric fence wire and cardboard toilet paper tubes.Schematics from hand me down handbooks and Popular Electronics.My elmer was my best friend(blind leading the blind)also a novice.My tools were a jackknife,rusty pliers and a wood burning iron with which I learned my first lesson about cold solder joints before a tv  repairman showed me the light and gave me  a real
soldering pencil with electrical solder in lieu of my previous supply of plumbers solder.My test equipment was a lightbulb and telegraph key with plenty of jumper clip wires.
  Needless to say my construction progress was a real cluster duck and for trouble shooting I learned to use the"lets try this part" substitution method and eventually I would get a tube to glow in a xtmr. or hear a cw tone  in a receiver that I had finally got working,this is all in between funny buzzing noises,smells,, smoke and sparks.This is also when I learned not to sit on a metal stool when building AC power supplies.To sum it all up if it had not been for the homebrewing experiences,feelings and pitfalls I probably would not be in the hobby today.
 



                        
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AA4HA
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« Reply #10 on: February 23, 2013, 07:02:14 PM »

Piftall Memories:
... This is also when I learned not to sit on a metal stool when building AC power supplies...

Oh, I learned that lesson the hard way too, after the second time of waking up on the floor I figured out that concrete is conductive to B+
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
W1JKA
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« Reply #11 on: February 24, 2013, 02:37:58 AM »

Re: AA4HA  Reply #10

Just curious Tisha,why did it take you two times? Wink

 
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K8AXW
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« Reply #12 on: February 24, 2013, 05:52:58 PM »

Quote
Just curious Tisha,why did it take you two times?

OMG!  I can't wait for this one!!   Roll Eyes
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